Influence of processing route and SiO 2 on sintering ability, CTE, and dielectric constant of β-Si 4 Al 2 O 2 N 6

• Published in: Journal of materials research 2008-09, Vol.23 (9), p.2305-2311
• Main Authors: Ganesh, Ibram, Thiyagarajan, N., Jana, D.C., Sundararajan, G., Olhero, S.M., Ferreira, J.M.F.
• Format: Article
• Language: English
• ISSN: 0884-2914; 2044-5326
• DOI: 10.1557/jmr.2008.0302

Dense β-Si 4 Al 2 O 2 N 6 and β-Si 4 Al 2 O 2 N 6 -0.5SiO 2 ceramics were obtained from α-Si 3 N 4 , α-Al 2 O 3 , AlN, and Y 2 O 3 upon sintering green bodies consolidated by aqueous gel casting. For comparison purposes, a β-Si 4 Al 2 O 2 N 6 was also prepared by the conventional dry-powder processing route. In the case of gel-cast β-Si 4 Al 2 O 2 N 6 , the as-purchased AlN powder was treated with H 3 PO 4 and Al(H 2 PO 4 ) 3 prior to use along with α-Si 3 N 4 , α-Al 2 O 3 , and Y 2 O 3 . The gel-cast β-Si 4 Al 2 O 2 N 6 exhibited superior hardness (1423 ± 6 Hv), fracture toughness (3.95 ± 0.3 MPa⋅m 1/2 ), and coefficient of thermal expansion (CTE) (3.798 × 10 −6 /°C between 30 and 1000 °C) in comparison to the ceramic consolidated by conventional dry pressing, which exhibited only 1317 ± 5 Hv, 3.30 ± 0.2 MPa⋅m 1/2 , and 3.532 × 10 −6 /°C between 30 and 700 °C. The in situ-generated ∼9 wt% SiO 2 has considerably reduced the dielectric constant and CTE of β-Si 4 Al 2 O 2 N 6 from 7.30 to 6.32 and from 3.798 × 10 −6 /°C to 3.519 × 10 −6 /°C, respectively. The loss tangent property of the investigated materials was little influenced by the variation of chemical composition and processing route.